US 7,742,392 B2Granted

Blind carrier frequency offset estimator based on single-OFDM-symbol PN ranging code in multi-user OFDMA uplink

AssigneeSTMicroelectronics (Beijing) R&D Co., Ltd.

InventorsYiqun Ge, Xutao Zhou, Wuxian Shi

Life of this patent

Estimating the term…

Abstract

A blind carrier frequency offset estimator is based on a single-OFDM-symbol training sequence in multi-user OFDMA uplink. Through multiple access interference modeling and analysis, a virtual user is employed that occupies the all null sub-carriers. By minimizing the energy leakage on the virtual user in term of tentative frequency offsets, the estimator can approach the real frequency offset. The estimator performs only on frequency-domain, simplifies interference calculations, and lowers the rank of the matrix. An iterative computation method is used to approach the real frequency offset.

Claims16

Dependent claims

A method for estimating a carrier frequency offset by an interleaved OFDMA system comprising:

initializing a carrier frequency offset to provide an initial carrier frequency offset;
initializing a cost function to provide an initial value of the cost function;
calculating a correction matrix on a current frequency value;
calculating a cost function using a calculated correction matrix value in a DSP integrated circuit to provide a calculated value of the cost function;
comparing the calculated value of the cost function to the initial value of the cost function;
if the calculated value of the cost function is greater than the initial value of the cost function, then the method is terminated and the initial carrier frequency offset is returned as the estimated carrier frequency offset;
if the calculated value of the cost function is less than the initial value of the cost function, then the calculated value is set as a new cost function initial value;
incrementally increasing the carrier frequency offset value;
and
repeating the correction matrix and cost function calculations until an estimated carrier frequency offset is returned, or until the range of the carrier frequency offset is exceeded,
wherein the correction matrix is calculated using one of the following two formulae:
I
⁡
(
u
,
v
)
=
{
sin
⁢
⁢
c
⁢
(
f
+
sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)
)
·
ⅇ
-
jπ
⁡
(
1
-
1
N
)
⁢
(
f
+
sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)
)

sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)

≤
d
0
else
wherein I(u,v) is an identity matrix;
c is a constant;
f is frequency;
sc(l) is the position index of user “l”;
u is an identity matrix entry;
v is an identity matrix entry;
sc(k) is the position index of user “k”;
N is the OFDM modulation size;
and
d is a predetermined distance;
and
J
(
ranging
)
⁡
(
f
)
=
(
R
M
(
nll
)
×
1
′
⁡
(
null
)
)
H
·
R
M
(
nll
)
×
1
′
⁡
(
null
)
=
(
R
(
null
+
ranging
)
)
H
·
(
C
(
ranging
)
⁡
(
f
)
)
H
·
C
(
ranging
)
⁡
(
f
)
·
R
(
null
+
ranging
)
wherein J is a cost function,
f is frequency;
R is a received frequency-domain signal vector;
R′ is a corrected received frequency-domain signal vector;
M is the number of available sub-carriers;
and
H is the Hermitian transpose.

192 more elements

An OFDMA system employing a method for estimating a carrier frequency offset, the method comprising:

initializing a carrier frequency offset to provide an initial carrier frequency offset;
initializing a cost function to provide an initial value of the cost function;
calculating a correction matrix on a current frequency value;
calculating a cost function using a calculated correction matrix value in a DSP integrated circuit to provide a calculated value of the cost function;
comparing the calculated value of the cost function to the initial value of the cost function;
if the calculated value of the cost function is greater than the initial value of the cost function, then the method is terminated and the initial carrier frequency offset is returned as the estimated carrier frequency offset;
if the calculated value of the cost function is less than the initial value of the cost function, then the calculated value is set as a new cost function initial value;
incrementally increasing the carrier frequency offset value;
and
repeating the correction matrix and cost function calculations until an estimated carrier frequency offset is returned, or until the range of the carrier frequency offset is exceeded,
wherein the correction matrix is calculated using one of the following two formulae:
I
⁡
(
u
,
v
)
=
{
sin
⁢
⁢
c
⁢
(
f
+
sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)
)
·
ⅇ
-
jπ
⁡
(
1
-
1
N
)
⁢
(
f
+
sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)
)

sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)

≤
d
0
else
wherein I(u,v) is an identity matrix;
c is a constant;
f is frequency;
sc(l) is the position index of user “l”;
u is an identity matrix entry;
v is an identity matrix entry;
sc(k) is the position index of user “k”;
N is the OFDM modulation size;
and
d is a predetermined distance;
and
J
(
ranging
)
⁡
(
f
)
=
(
R
M
(
nll
)
×
1
′
⁡
(
null
)
)
H
·
R
M
(
nll
)
×
1
′
⁡
(
null
)
=
(
R
(
null
+
ranging
)
)
H
·
(
C
(
ranging
)
⁡
(
f
)
)
H
·
C
(
ranging
)
⁡
(
f
)
·
R
(
null
+
ranging
)
wherein J is a cost function;
f is frequency;
R is a received frequency-domain signal vector;
R′ is a corrected received frequency-domain signal vector;
M is the number of available sub-carriers;
and
H is the Hermitian transpose.

192 more elements

Dependencies are inferred from the claim text.

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Abstract

A method for estimating a carrier frequency offset by an interleaved OFDMA system comprising:

initializing a carrier frequency offset to provide an initial carrier frequency offset;
initializing a cost function to provide an initial value of the cost function;
calculating a correction matrix on a current frequency value;
calculating a cost function using a calculated correction matrix value in a DSP integrated circuit to provide a calculated value of the cost function;
comparing the calculated value of the cost function to the initial value of the cost function;
if the calculated value of the cost function is greater than the initial value of the cost function, then the method is terminated and the initial carrier frequency offset is returned as the estimated carrier frequency offset;
if the calculated value of the cost function is less than the initial value of the cost function, then the calculated value is set as a new cost function initial value;
incrementally increasing the carrier frequency offset value;
and
repeating the correction matrix and cost function calculations until an estimated carrier frequency offset is returned, or until the range of the carrier frequency offset is exceeded,
wherein the correction matrix is calculated using one of the following two formulae:
I
⁡
(
u
,
v
)
=
{
sin
⁢
⁢
c
⁢
(
f
+
sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)
)
·
ⅇ
-
jπ
⁡
(
1
-
1
N
)
⁢
(
f
+
sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)
)

sc
(
l
)
⁡
(
u
)
-
sc
(
k
)
⁡
(
v
)

≤
d
0
else
wherein I(u,v) is an identity matrix;
c is a constant;
f is frequency;
sc(l) is the position index of user “l”;
u is an identity matrix entry;
v is an identity matrix entry;
sc(k) is the position index of user “k”;
N is the OFDM modulation size;
and
d is a predetermined distance;
and
J
(
ranging
)
⁡
(
f
)
=
(
R
M
(
nll
)
×
1
′
⁡
(
null
)
)
H
·
R
M
(
nll
)
×
1
′
⁡
(
null
)
=
(
R
(
null
+
ranging
)
)
H
·
(
C
(
ranging
)
⁡
(
f
)
)
H
·
C
(
ranging
)
⁡
(
f
)
·
R
(
null
+
ranging
)
wherein J is a cost function,
f is frequency;
R is a received frequency-domain signal vector;
R′ is a corrected received frequency-domain signal vector;
M is the number of available sub-carriers;
and
H is the Hermitian transpose.

192 more elements